Modeling the kinematics and Dynamics of Compliant Contact

In this paper, we discuss the modeling of the kinematics and dynamics of compliant contact between bodies moving in Euclidean space. First, we derive the kinematic equations describing the motion of the contact point when two rigid bodies are rolling on each other. Secondly, we extend these results to describe the motion of the closest points between two rigid bodies moving freely in space. Then, we use these results to model compliant contact between bodies, using a spatial spring and a damper to model energy stored and dissipated during contact

Characterization of stiction effects of an electrostatic micro positioner for probe storage

We start by presenting a short explanation of the micro actuator working principle. The main contribution of this paper is the characterization of the coefcient of stiction between two silicon nitride parts of a MEMS actuator. Having one at contact surface while the other is composed of many relatively sharp circular bumps, has the advantage that the effective contact area is drastically reduced. The stiction coefcient varies between 0-0.53 for the device conguration presented. The exact value depends closely on the electrostatically applied force which presses the textured part on to the smooth one. Individual measurements used are highly accurate (typically within 5 nm noise band) and identical measurements for the characterization of stiction show only a small variation, typically under 25nm on a range of 11.8m

Energy Conservative Limit Cycle Oscillations

This paper shows how globally attractive limit cycle oscillations can be induced in a system with a nonlinear feedback element. Based on the same principle as the Van der Pol oscillator, the feedback behaves as a negative damping for low velocities but as an ordinary damper for high velocities. This nonlinear damper can be physically implemented with a continuous variable transmission and a spring, storing energy in the spring when the damping is positive and reusing it when the damping is negative. The resulting mechanism has a natural limit cycle oscillation that is energy conservative and can be used for the development of robust, dynamic walking robots

Control of walking robots using virtual springs

At the Control Engineering group of the University of Twente, we are conducting research on control of bipedal robots. In our search for robust and energy efficient control, we are making extensive use of simulation. In order to facil- itate the development of algorithms, we want to design con- trollers that work in a space of “meaningful variables”; i.e. we don’t control joint angles directly but we control things as “position and velocity of center of mass”, “shape of the robot’s locked inertia ellipsoid” [1] and “foot position”

Coordinate transformation as a help for controller design in walking robots

For walking robots, the robot’s absolute position must be re- flected in the state. Usually one chooses to include the pose and velocity of the torso in the state (i.e., the torso is taken as the reference body). However, sometimes it is useful to choose a different reference body; in particular the stance foot is a good choice

Stiffness and position control of a prosthetic wrist by means of an EMG interface

In this paper, we present a novel approach for decoding electromyographic signals from an amputee and for interfacing them with a prosthetic wrist. The model for the interface makes use of electromyographic signals from electrodes placed in agonistic and antagonistic sides of the forearm. The model decodes these signals in order to control both the position and the stiffness of the wrist